1. Field of the Invention
The invention relates to a feed device for injection molding machines, particularly for polyester processing, consisting of a feed ram and a feed cylinder for receiving the plastic material to be processed, which is fed into hollow cylindrical material containers of the feed device.
Such feed devices are used mainly for fully automatic compression and injection molding of polyester materials with high material throughput and serve the purpose of emptying the polyester material, fed in doughlike condition into the material containers, into the feed cylinder of the injection molding machine, from there to be pressed into the plasticizing unit of the injection molding machine with the aid of the feed ram.
2. Description of the Related Art
The technique of arranging several filled material containers above one another in a lifting device and feeding them to a discharge station is known. The hollow cylindrical material containers are open on their front ends and reach the discharge station in a horizontal position with the aid of the lifting device. The discharge station consists of a horizontally sliding discharge piston which, to empty the material container, enters the hollow cylindrical interior of the material container from the front and pushes the polyester material out. The discharge station is placed above the feed cylinder of the injection molding machine so that when the discharge piston pushes through, the material passes through the material container into the vertical feed cylinder which is open on the upper front side. By lowering the feed ram into the feed cylinder, the material is pressed into the plasticizing cylinder of the injection molding machine.
The disadvantage of this known embodiment is that, in addition to the feed ram, another special discharge piston is necessary through which the material is brought into the feed cylinder. This necessitates large space requirements on the injection molding machine and considerable building expense, which raises the capital cost of the unit. In addition, the time between feeding the material into the material container and discharging is rather long, so that the material is exposed to harmful environmental influences to a greater extent. Moreover, the sensitive material is brought into contact first with the piston surface of the discharge piston and then with the piston surface of the feed ram. This impairs the quality of the material and raises the risk of contamination. Even the cleaning expense for the parts of the unit which come into contact with the sticky polyester material is very high with the known unit due to the use of two feed rams. This proves very disadvantageous especially during a material changeover.